The present invention refers to a sample fluid testing device and a method for analyzing a sample fluid, using a test media tape.
Sample fluid testing devices are used e.g. by diabetics for regularly testing samples of their blood to determine the level of blood glucose. In one known type of fluid testing devices, disposable test strips are used to test the sample fluid, each test strip comprising a sensor field, which contains a reagent material that will react with an analyte within the sample fluid. One possibility well-known in the art for analyzing the sample fluid on the sensor field is an electrochemical analysis. For the electrochemical analysis, electrical signals produced within the sensor field which contains the sample fluid are relayed from electrodes within the sensor field to a meter via electrically conductive tracks, the meter being part of the sample fluid testing device. After the measurement has been taken, the test strip is disposed of.
Other known types of fluid testing devices contain test media cassettes with a plurality of sensor fields on a test media tape, the test media tape being provided on a reel within the test media cassette.
WO 2004/056269 A1 is directed towards a body fluid testing device for analyzing a body fluid, comprising: a test media tape adapted to collect the body fluid, said test media tape comprising a tape and test media portions, wherein a free tape portion without test medium is located between successive test media portions. The testing device further comprises a supply portion, which comprises a housing in which an uncontaminated test media tape is contained, the housing further having an opening for withdrawing the test media tape from the housing. The supply portion further has a sealing means for closing the opening against the surrounding. A free tape portion of the test media tape is located between a surface (typically a wall of the housing) and the sealing means when the sealing means closes the opening.
EP 1 424 040 A1 relates to a body fluid testing device for analyzing a body fluid, comprising: a test media tape adapted to collect the body fluid, a supply portion storing an uncontaminated section of the test media tape, a storage portion for storing a contaminated section of the test media tape, an exposure portion positioned between the supply portion and the storage portion, the exposure portion being adapted to expose a section of the test media tape to the body fluid. The exposure portion has a tip portion for exposing a test medium to body fluid application.
For electrochemically analyzing a sample fluid on such a test media tape, an electrical contact from a meter within the sample fluid testing device to the sensor fields on the test media tape has to be established. One known solution for establishing this contact is e.g. described in WO 01/23885 A1. This document refers to a test device for testing of analyte concentration in a fluid to be applied thereto, the device comprising a plurality of sensors on a reel, each of the sensors carrying reagent means for producing an electrical signal in response to the concentration of analyte in an applied fluid. Each of these sensors has a plurality of electrodes, corresponding electrodes of adjacent sensors being connected together by a conductive track on the reel. The device further comprises a meter with electronic means for producing a signal output which is dependent on the electrical signal from the sensors. The meter has contacts, which are electrically connected with the conductive tracks. In this test device, all the sensors are connected by the conductive track, the meter also being permanently connected to the conductive track. The application of a sample fluid to any of the sensors will produce an electrical signal, which is detectable by the meter. A used sensor can be separated from the end of the reel, before a subsequent measurement is taken in order to prevent the generation of electrical signals by the used sensor during the subsequent measurement.
Another example for a sample fluid testing device with such a solution for the electrical contact between the sensor fields and the meter is described in US 2005/0230253 A1.
One disadvantage of this solution is that the long conductive track connecting the electrodes of adjacent sensors has a high resistance, which above all is altered, when the individual sensors are separated from the reel. Furthermore, the unused sensors are not totally passive and can produce interfering signals, which are not related to the analyzed sample fluid. Moreover, the separated sensors are contaminated with the sample fluid and have to be safely discarded, whereas a continuous test media tape, from which the used sensors are not separated, could be stored conveniently on a reel within a waste portion of the test media cassette.
U.S. Pat. No. 5,395,504 A therefore proposes a test media tape with a plurality of separately arranged sensors, which are contacted successively. The contact of each sensor with an electronic circuit is provided by means of resilient foils coming into contact with zones of contact of the sensor by means of a slide connection. One drawback of a slide connection is, that the sliding of the slide contacts over the surface of the moving test media tape when the next sensor is to be used can damage the elements on the surface of the test media tape, e.g. electrodes or conductive tracks made of very thin metal layers (approximately 50 nm).
WO 2005/047861 A2 discloses a biochemical analysis instrument for multiple fluid analysis including a housing, a sensor for sensing a reaction disposed in the housing, an aperture formed in the housing and a test tape housing area formed in the housing. The sensor is disposed to selectively move within the housing area, the aperture being formed to provide access to this tape housing area. The instrument further includes a cassette configured to be received within the tape housing area. The cassette includes a case, a first chamber formed in the case, a second chamber formed in the case, a gap formed in the case, wherein the first chamber and the second chamber are disposed at a respective side of the gap. A test tape is disposed within the housing, which extends from the first chamber across the gap to the second chamber, the test tape having a plurality of active zones disposed at predetermined spaced intervals along the tape for testing an analyte. An electrode based sensor head can be moved forward to contact the test tape and retracted into its original lower non-contact position. Such a solution for contacting the sensors requires a complex construction of the sample fluid testing device to enable the movement of the sensor head and the test tape and to detect their relative positions.